Field of the Invention
The present invention relates to microscopy and other forms of imaging using coherent light. In particular, the present invention relates to coherent diffractive imaging (CDI) with an arbitrary angle of incidence.
Discussion of Related Art
Coherent diffractive imaging (CDI), for example ptychography, is an emerging technique that enables wavelength- and diffraction-limited imaging. FIG. 1A (Prior Art) shows a conventional 2-dimensional transmission CDI system, where incident radiation 10 illuminates object 11 with a normal incidence, and transmitted scattering field 12 is measured on detector 13.
FIG. 1B (Prior Art) shows a conventional 2-dimensional reflection CDI, where the incident radiation before reflection 14 reflects off of mirror 15 as incident radiation 10 and illuminates object 11 with near-normal incidence (the angle of incidence 17 θi is close to 0 degrees).
FIG. 1C shows CDI in a reflection geometry with grazing incidence (the angle of incidence 17 θi is close to 90 degrees). With non-normal incidence, there is apparent distortion in the measured diffraction pattern, and a method that corrects the distortion was introduced in prior art (see, for example, Gardner, D. F. et al., Opt. Express 20, 19050-9, 2012). In this method, the spatial frequency is calculated for each position on the detector, and then the scatter pattern is remapped from the calculated non-uniform frequency grid to a uniform frequency grid. This method is time consuming because it requires remapping from a non-uniform grid to a uniform grid, which typically involves triangulation.
The fact that conventional CDI is limited to the above configurations brings several disadvantages: 1) it limits the freedom of the imaging geometry; 2) for reflection CDI, it results in a narrow range of scattering available for detection, leading to low resolution in the reconstructed image; 3) the reflectivity of objects might be low at near-zero degrees incidence. A need remains in the art for methods and apparatus to enable CDI with arbitrary angle of incidence and efficient computation.